(a) Field of the Disclosure
The present disclosure relates to an automatic transmission for a vehicle. More particularly, the present disclosure relates to a planetary gear train of an automatic transmission for a vehicle.
(b) Description of the Related Art
Generally, an automatic transmission achieving more speed stages has been developed to enhance fuel economy and optimize drivability. Increases in oil prices may make enhancing fuel consumption of a vehicle important.
Therefore, research into reducing weight and enhancing fuel economy through downsizing of an engine and for securing drivability and fuel economy through multiple speed stages of automatic transmissions has been conducted.
However, in an automatic transmission, as the number of speed stages increases, the number of internal components (particularly, planetary gear sets) increases. As a result, the lengh of the transmission increases. Therefore, mountability, cost, weight, transmission efficiency, and the like may deteriorate.
In recent years, 8-speed automatic transmissions have been implemented. Research and development of a planetary gear train capable of implementing more speed stages has also been actively conducted.
However, a conventional 8-speed automatic transmission typically includes three to four planetary gear sets and five to seven control elements (frictional elements). In this case, since the length of the automatic transmission increases, mountability may deteriorate.
In recent years, a planetary gear train may be orientated where one planetary gear set is disposed above another planetary gear set, but structures of automatic transmissions in which parallel planetary gear sets are applied are very limited.
In another instance, dog clutches are used, instead of control elements of a wet-type. In this instance, however, shift feel can deteriorate.
The above information disclosed in this Background section is only to enhance the understanding of the background of the disclosure and therefore the background may contain information that is not prior art that is already known to a person of ordinary skill in the art.